A radio access network (Radio Access Network, hereinafter referred to as RAN) includes a GSM enhanced data rate for GSM evolution radio access network (GSM Enhanced Data Rate for GSM Evolution Radio Access Network, hereinafter referred to as GERAN), a universal mobile telecommunications system territorial radio access network (Universal Mobile Telecommunications System Territorial Radio Access Network, hereinafter referred to as UTRAN), and an evolved universal mobile telecommunications system territorial radio access network (Evolved UMTS Territorial Radio Access Network, hereinafter referred to as E-UTRAN).
A user equipment (User Equipment, hereinafter referred to as UE) first completes combined registration on the GERAN/UTRAN. The UE then moves to the E-UTRAN, completes combined update and activates an idle mode signaling reduction function (Idle mode signalling reduction, hereinafter referred to as ISR). When the UE moves to the GERAN/UTRAN again and camps on the GERAN/UTRAN, the UE may be implicitly detached by a mobile switch center/visitor location register (Mobile Switch Center/Visitor Location Register, hereinafter referred to as MSC/VLR).
The inventor finds that, in the prior art, when the foregoing scenario occurs, a UE under normal network coverage does not sense that the UE is implicitly detached by an MSC/VLR, which may cause that, after the UE is detached by the MSC/VLR, a mobile terminated service is unreachable, thereby affecting service experience of a user.